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Cultivating organic cannabis with living soil

"Organic cannabis hits different. When properly grown and cured, the complexity of flavor and effect is hard to beat," says Stewart Maxwell in his latest article on Elevated Botanist. "This aesthetic difference can be attributed to the diversity of nutrients and probiotics available in living soils. Nutrient diversity fuels the biosynthesis of complex compounds like terpenes and flavonoids that contribute to cannabis quality. Growing organic cannabis is not rocket science, but there is some science involved. The basics of growing in living soils is the same if you are growing five plants or five acres. If you invest a bit of time to better understand what is happening in the root zone, your quality and yields will improve."

Living soil
Plants have co-evolved with soil microorganisms for millions of years. Cultivation systems that leverage these ancient relationships are known as living soil systems. For small scale growers, organic cultivation doesn’t need to be complicated. Cannabis plants have been growing in living soils since long before we showed up and will thrive in fertile garden beds. If you are growing in containers, start with the best potting soil you can find, or make your own living soil mix.
Growing in organic soil is also a cost-effective way to cultivate distinctive cannabis at commercial scale in a market flooded with mediocre weed. Consumers might not appreciate the complexities of cultivation systems, but they vote with their dollars, and organic herb is in high demand.

Root exudates
During photosynthesis, plants absorb carbon dioxide, and make carbohydrates. Up to 40% of this energy is shared with soil microbes as root exudates. These carbon rich exudates are composed of simple sugars, and organic and amino acids. Most microorganisms don’t have access to atmospheric carbon and provide plants with nutrients and other benefits in exchange for this valuable energy source. Plants can influence soil PH and share exudates selectively with the microbial communities that provide for their needs. Roots, soil, and microbes create a densely populated habitat known as the rhizosphere.

Soil food web
The soil food web is composed of interconnected kingdoms of life that cooperate, compete, and consume each other.

  • Bacteria:These single celled organisms are abundant in healthy soils, and populations can double every 15 minutes.
  • Fungi: Fungi form hyphal networks which enable nutrient transport within the soil and communication between plants.
  • Nematodes: Nematodes are microscopic worms, many of which feed on plant roots.
  • Protozoa: Protozoa are microbes that swim through soil water, feeding on bacteria.
  • Worms: earthworms consume decaying materials and inoculate them with beneficial gut bacteria.
  • Insects: Many insects spend part of their lifecycle in the soil. Some of these are detritivores, and consume decaying materials, others are herbivores and can emerge from the soil to feed on your plants.

Suppressive soil
Healthy soil makes healthy plants. For organic growers, a balanced and diverse soil biome plays an important role in pest suppression. Microbes can suppress pests and disease in many ways:

  • Competition: Beneficial microorganisms can outcompete pathogens for food sources and physical habitat.
  • Parasitism: Bacterial and fungal microbes can parasitize plant pests including nematodes and soil dwelling insects.
  • Chemical Warfare: Some microbes produce metabolites and volatile organic compounds that inhibit pathogen growth.
  • Immune Response: Microorganisms can solicit plant immune responses through hormone signaling pathways.
  • Predation: Some bacteria practice wolf pack predation to feed on outnumbered prey.

Soil chemistry can also contribute to pest suppression. Nutrients like Silicon and Chitosan strengthen cell walls and aid chemical defense.

Cannabis nutrients
Cannabis is a heavy feeder and is often cultivated in controlled environments. The economics of these growing conditions favor high planting densities, and short crop cycles. In addition to the initial nutrient charge provided by living soil, supplemental feedings during crop development can improve plant performance, and enables use of lower soil volumes. Slow-release organic nutrients can be supplied by compost and dry amendments. Liquid or soluble nutrients can also be fed during periods of rapid crop growth.

Liquid nutrients 
Many organic fertilizers are biostimulants which provide plant health benefits in addition to available nutrients. Cold processed kelp inputs are rich sources of plant growth factors, such as cytokinins. These naturally occurring hormones benefit plant development and stress coping. Fish hydrosolate fertilizers are great sources for amino acids and beneficial bacteria. Plants make amino acids from Nitrogen, but they can also uptake them directly from the soil and save the energy. Soluble organic nutrients are usually micronized to increase surface area and can be suspended in a liquid solution. Organic fertilizers should never be fed through irrigation systems or biofilm will accumulate and ruin your day.

Soil amendments
Dry inputs are usually incorporated into soil mixes or applied early in the crop cycle to provide sustained fertility. Protein meals are organic amendments with a high nutrient density. These products have been dried and milled to increase their bioavailability and storage life. Mineral inputs are mined from natural deposits. Some of these inputs require a long time to mineralize and are better incorporated into organic mixes prior to planting. Dry amendments can be blended to make slow-release fertilizers with specific nutrient ratios based on  crop needs. Mineralization of dry inputs requires water availability. Fertilizer spikes can be applied by opening the soil profile with a knife and inserting dry blends for contact with soil water. Nutrient amendments can also be top dressed on the soil surface. Mulch application and surface irrigation provide water for mineralization.

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